The invention is concerned with the technology of continuous strip annealing furnaces. Such furnaces are used in continuous annealing lines or in continuous galvanizing lines, yet the invention may be applied to other types of installations in which the strips are continuously treated, in particular in varnishing, coating and painting installations.
The method hinges around one or more strip annealing furnaces which consist of several sections equipped to perform consecutively the various phases of the heat-treatment cycle which are, in the simplest case: heating, holding and cooling.
At the end of each of the phases, the temperature reached by the product is determined and must be stabilized in order to obtain the required metallurgical characteristics. In particular, the temperature at the end of heating is very precise.
The operation is easy and is currently executed when the furnace operates in steady-state; it treats a product of given dimensions at a constant speed and according to an established heat-treatment curve.
Known industrial furnaces work daily with strips of different thickness and width in annealing cycles which are also variable.
Inevitably, transitional periods result during which the annealing temperature is difficult to reach and control in current heating chambers. The latter generally use traditional radiation or naked flame sources, and both are characterized by their significant thermal inertia.
The users have introduced measures which make it possible to reduce the duration and amplitude of the variations in annealing temperature during transitional periods of changing strip size.
The use of computers, dedicated to conducting these methods which follow the thermal state of the furnace in real time and control the change in the heating parameters and in the treatment speed, has afforded a partial solution to the problems.
In fact, these procedures introduce variations in treatment speed in the essential heating phase which affect the running and the performances of the other parts of the furnace or of the installation, such as in particular the cooling section or the coating section of a galvanizing line.